A method for establishing a traction transmission system model for low-pressure pantograph-catenary arcing

Abstract

The invention discloses a method for establishing a traction transmission system model of a low-pressure bow-net arc effect, which relates to the technical field of electrical engineering and comprises the following steps: correcting arc dissipation power, establishing an improved Schwarz low-pressure arc electrical characteristic model, establishing an electric locomotive traction transmission system model, and building a low-pressure bow-net arc effect traction transmission system model and performing simulation analysis; the invention aims at the bow-net offline arc phenomenon in the operation of a high-speed train, considers the dynamic process from the generation to the evolution of the bow-net offline arc, and establishes a low-pressure bow-net arc effect traction transmission system model suitable for a high-altitude low-pressure environment based on the electrical circuit structure of the high-speed train, which can accurately analyze the influence of the bow-net offline arc on the electrical characteristics of the high-speed train on-board transformer and traction converter under different altitude pressures, and obtains the voltage harmonic conditions at different stages, which can accurately reflect the actual operating conditions of the traction transmission system under the high-altitude low-pressure environment.

Description

Technical Field

[0001] The present invention relates to the field of electrical engineering technology, and in particular to a method for establishing a low-pressure pantograph-catenary arc action traction drive system model. Background Art

[0002] The pantograph-catenary system plays a vital role in the operation of electrified railways. It is the key bridge connecting the power supply system and the electric locomotive. The offline operation of the pantograph-catenary system will cause the pantograph-catenary arc, which will make the train receive current intermittently and burn the pantograph slide plate, generate radiated electromagnetic noise, and affect the safe and stable operation of the traction drive system. In the high-altitude and low-pressure environment, the generation of the pantograph-catenary arc is different from that in the plain environment, and the impact on the train traction drive system may also be different. Therefore, studying the impact of the pantograph-catenary arc on the train traction drive system in the high-altitude and low-pressure environment is of great reference value to the construction of the Sichuan-Tibet Railway and other railways in high-altitude and high-altitude areas.

[0003] At present, relevant research has been carried out at home and abroad on the influence of bow-catenary arc on traction transmission system. However, in the traditional offline analysis of the bow-catenary system, the influence of air pressure is not considered when conducting the influence of bow-catenary offline on the traction transmission system. Only the influence of bow-catenary offline on the traction transmission system under traditional plain conditions is analyzed. There are limitations, and it is impossible to accurately reflect the actual operating conditions of the traction transmission system under high-altitude and low-pressure environment. Therefore, the present invention proposes a method for establishing a traction transmission system model of low-pressure bow-catenary arc effect to solve the problems existing in the prior art. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to propose a method for establishing a traction transmission system model under the action of low-pressure bow-net arc, so as to solve the problem that in the traditional offline analysis of the bow-net system, the influence of air pressure is not considered when the bow-net offline analysis affects the traction transmission system, and only the influence of the bow-net offline on the traction transmission system under traditional plain conditions is analyzed, which has limitations and cannot accurately reflect the actual operating conditions of the traction transmission system in a high-altitude and low-pressure environment.

[0005] In order to achieve the purpose of the present invention, the present invention is implemented by the following technical scheme: a method for establishing a low-pressure pantograph-catenary arc action traction transmission system model, comprising the following steps:

[0006] Step 1: Based on the classic Schwarz arc model, the arc dissipation power is corrected by combining the air pressure environment parameters, running speed, arc length parameters and arc temperature parameters of the train in high altitude areas;

[0007] Step 2: Based on the classic Schwarz arc model, establish the relevant equations of the arc of the train bow network at different air pressures at high altitudes, that is, the improved Schwarz low-pressure arc electrical characteristic model;

[0008] Step 3: Taking the actual train EMU as a reference, combined with the traction braking characteristics of the EMU and the technical parameters of various components including the on-board transformer, rectifier, inverter and three-phase load, establish the electric locomotive traction drive system model;

[0009] Step 4: Combine the improved Schwarz low-pressure arc electrical characteristic model with the electric locomotive traction drive system model, build a low-pressure pantograph-catenary arc traction drive system model and perform simulation analysis to obtain the impact of the pantograph-catenary arc on the train traction drive system under high-altitude and low-pressure conditions.

[0010] A further improvement is that in step 1, the formula of the classic Schwarz arc model is:

[0011]

[0012] Where d is the arc diameter, g is the arc conductivity, t is the time, τ is the constant coefficient of the arc time constant, a is the conductivity index of the arc time constant, P loss is the dissipated power, b is the conductivity index of the dissipated power, u is the instantaneous value of the arc voltage, and i is the instantaneous value of the arc current.

[0013] A further improvement is that in step 1, the specific steps of correcting the arc dissipated power are: firstly analyzing the atmospheric pressure data of different regions, and obtaining the relationship between the altitude H and the air pressure P as follows:

[0014] H=45.1×[1-(P / P0) 0.1866 ]

[0015] Among them, P0 is the atmospheric pressure in the plain area. As the air pressure decreases, the arc diameter increases. The relationship between the two is as follows:

[0016]

[0017] During the arc burning process, the arc dissipated power p loss The conducted power p t , Convection heat dissipation power p k and the radiated power p s The corresponding expression is:

[0018] p loss =p t +p k +p s

[0019] Since the arc burning freely in the atmosphere will dissipate most of its heat energy through the convection mechanism, this process accounts for more than 80% of the total heat loss, while the heat conduction and radiation losses of the arc account for a relatively small proportion, so the power transmission and radiation power losses are ignored. When the pantograph is separated from the contact network, the front end of the high-speed train meets the air, resulting in air compression, that is, the air is compressed at the front end of the train to produce a high-pressure area. The high-pressure air then rapidly diffuses to the sides and top of the vehicle, forming lateral and rising airflows, further strengthening the convection heat dissipation of the pantograph-catenary arc. Therefore, the convection heat dissipation power is regarded as the dissipation power of the pantograph-catenary arc, that is:

[0020] p loss =p k

[0021] Based on the arc blowing theory, the arc blowing direction is classified as horizontal blowing when the airflow is perpendicular to the axial direction of the arc, and longitudinal blowing when the airflow is parallel to the arc direction. During the train operation, the arc is perpendicular to the train operation direction and is mainly affected by horizontal arc blowing. Therefore, the influence of longitudinal arc blowing on the electrical characteristics of the bow-catenary arc is ignored. Assuming the train speed is v, the arc diameter is d, and the volume flowing through the arc length per hour is vdl, at this time, the air temperature rises from the initial temperature T0 to the average temperature T of the arc. c , convection heat dissipation power p k equal:

[0022]

[0023] Under standard atmospheric pressure, c is expressed as:

[0024]

[0025] Substitute c into the convection heat dissipation power p k Formula, we get:

[0026]

[0027] Wherein, v represents the moving speed of the train, in cm / s, d represents the arc column diameter, in cm, and l represents the arc length, in cm;

[0028] After unit conversion, we get:

[0029]

[0030] Among them, p loss is the heat loss, v is the train speed, d is the arc diameter, l is the arc length, T h is the maximum temperature of the arc column when the arc is burning, T l It is the lowest temperature of the arc column when the arc is burning, and T0 is the temperature when the fluid medium is not in contact with the arc.

[0031] A further improvement is that in step 2, the improved Schwarz low-pressure arc electrical characteristic model formula is:

[0032]

[0033] Where, v is the train speed, g is the arc conductivity, τ is the arc time constant coefficient, a is the conductivity index of the arc time constant, u is the instantaneous value of the arc voltage, i is the instantaneous value of the arc current, d is the arc diameter, l is the arc length, T h is the maximum temperature of the arc column when the arc is burning, T l It is the lowest temperature of the arc column when the arc is burning, and T0 is the temperature when the fluid medium is not in contact with the arc.

[0034] Further improvement lies in: in the step three, the actual train EMU used as reference is the CRH2 EMU, the CRH2 EMU adopts an ATM9 transformer, the rectifier of the CRH2 EMU adopts a single-phase three-level PWM pulse rectifier, the inverter of the CRH2 EMU adopts a three-level inverter, and the rectifier, supporting capacitor and inverter are integrally packaged into a traction inverter.

[0035] Further improvement lies in: in the step four, during the simulation analysis, two typical operating conditions encountered when the train is running at a constant speed and the bow-catcher is offline are determined. In the first typical operating condition, the bow-catcher offline time is set to 100ms, and the bow-catcher arc continues to burn during the offline process. In the second typical operating condition, the bow-catcher offline time is set to 400ms, and the power dissipation of the bow-catcher arc gradually increases during the offline process.

[0036] Further improvements are as follows: according to the two typical working conditions determined, the short-term offline time of the bow network is set to 100ms, and the long-term offline time of the bow network is set to 400ms respectively; according to the starting time of the motor, the bow network offline time t=0.5s is set, and the offline recovery times are t=0.6s and t=0.9s respectively; three air pressure environments of P0=101.3kPa, P=70.6kPa, and P=50.5kPa are set, and the influence of the bow network arc on the waveform of the high-voltage side voltage of the on-board transformer and the rectifier output voltage changing with time under three air pressure levels is simulated.

[0037] Further improvements are as follows: under the condition that the model parameters of the traction transmission system with low-pressure pantograph-catenary arcing are the same, a fast Fourier transform analysis is performed on the high-voltage side voltage of the on-board transformer under the condition of the pantograph-catenary offline time of 400ms at the air pressure levels of 101.3kPa, 70.6kPa and 50.5kPa respectively.

[0038] The beneficial effects of the present invention are as follows: the present invention is based on the classic Schwarz arc model, combined with the special natural environment of train operation in plateau low-pressure areas, and targets the bow-net offline arc phenomenon in high-speed train operation. The dynamic process of the bow-net offline arc from generation to evolution is considered, and relying on the electrical circuit structure of the high-speed train, a low-pressure bow-net arc action traction transmission system model suitable for high-altitude and low-pressure environments is established. The influence of the bow-net offline arc on the electrical characteristics of the high-speed train on-board transformer and traction converter under different altitude pressures can be accurately analyzed, and the voltage harmonics at different stages can be obtained. The actual operating conditions of the traction transmission system can be accurately reflected in the high-altitude and low-pressure environment, and it has certain reference value for railway construction and maintenance in high-altitude areas, and it helps to ensure the stable operation of the train traction transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 It is a flow chart of a method for establishing a low-pressure pantograph-catenary arc action traction transmission system model of the present invention;

[0041] Figure 2 1 is a schematic diagram of the waveform of the arc voltage of the Schwarz model bow-catenary under different gas pressures in an embodiment of the present invention;

[0042] Figure 3 is a principle block diagram of a high-speed train traction drive system in an embodiment of the present invention;

[0043] Figure 4 It is a waveform diagram of the voltage on the high-voltage side of the on-board transformer changing with time at different air pressure levels when the pantograph-network offline time is 100ms in an embodiment of the present invention;

[0044] Figure 5 It is an enlarged diagram of the voltage waveform on the high-voltage side of the on-board transformer during the off-line arcing process of the bow-net in the embodiment of the present invention;

[0045] Figure 6 It is a waveform diagram of the voltage on the high-voltage side of the on-board transformer changing with time at different air pressure levels when the pantograph-network offline time is 400ms in the embodiment of the present invention;

[0046] Figure 7 This is an enlarged diagram of the voltage waveform on the high-voltage side of the on-board transformer during the arc extinction process in an embodiment of the present invention;

[0047] Figure 8 is a waveform diagram of the DC side voltage changing with time in a short-time offline state in an embodiment of the present invention;

[0048] Fig. 9 is a waveform diagram of the DC side voltage changing with time in a long-term offline state in an embodiment of the present invention;

[0049] Fig.10 2. It is a schematic structural diagram of a low-pressure pantograph-catenary arc-action traction transmission system model in an embodiment of the present invention;

[0050] Fig.11 Schematic diagram of voltage harmonic distribution on the high-voltage side of the on-board transformer at different pressure levels in the initial arcing stage in an embodiment of the present invention;

[0051] Fig.12 Schematic diagram of voltage harmonic distribution on the high-voltage side of the on-board transformer at different pressure levels in the stable arcing stage in an embodiment of the present invention;

[0052] Fig.13 Schematic diagram of voltage harmonic distribution on the high-voltage side of the on-board transformer at different pressure levels in the arc extinction stage in an embodiment of the present invention;

[0053] Fig.14 It is a schematic diagram of the variation trend of the total harmonic distortion rate of the high-voltage side voltage of the traction drive system transformer at different arcing stages in an embodiment of the present invention. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] See also Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Fig. 9 , Fig.10 This embodiment provides a method for establishing a low-pressure pantograph-catenary arc action traction transmission system model, comprising the following steps:

[0056] Step 1: Correct the arc dissipation power

[0057] In a high-altitude environment, arc parameters change, thus affecting the size of arc dissipation power. This embodiment is based on the classic Schwarz arc model and combines the air pressure environment parameters, running speed, arc length parameters and arc temperature parameters of trains in high-altitude areas to calibrate the arc dissipation power. The specific steps are: firstly, analyze the atmospheric pressure data of different regions to obtain the relationship between the altitude H and the air pressure P as follows:

[0058] H=45.1×[1-(P / P0) 0.1866 ]

[0059] Among them, P0 is the atmospheric pressure in the plain area, which is 101.3kPa. As the air pressure decreases, the arc diameter increases. The relationship between the two is as follows:

[0060]

[0061] The high-speed running of the train will generate a large airflow, resulting in the dissipation of power mainly through convection. During the arcing process, the arc dissipation power p loss The conducted power p t , Convection heat dissipation power p k and the radiated power p s The corresponding expression is:

[0062] p loss =p t +p k +p s

[0063] Since the arc burning freely in the atmosphere will dissipate most of its heat energy through the convection mechanism, this process accounts for more than 80% of the total heat loss, while the heat conduction and radiation losses of the arc account for a relatively small proportion, so the power transmission and radiation power losses are ignored. When the pantograph is separated from the contact network, the front end of the high-speed train meets the air, resulting in air compression, that is, the air is compressed at the front end of the train to produce a high-pressure area. The high-pressure air then rapidly diffuses to the sides and top of the vehicle, forming lateral and rising airflows, further strengthening the convection heat dissipation of the pantograph-catenary arc. Therefore, the convection heat dissipation power is regarded as the dissipation power of the pantograph-catenary arc, that is:

[0064] p loss =p k

[0065] Based on the arc blowing theory, the arc blowing direction is classified as horizontal blowing when the airflow is perpendicular to the axial direction of the arc, and longitudinal blowing when the airflow is parallel to the arc direction. During the train operation, the arc is perpendicular to the train operation direction and is mainly affected by horizontal arc blowing. Therefore, the influence of longitudinal arc blowing on the electrical characteristics of the bow-catenary arc is ignored. Assuming the train speed is v, the arc diameter is, and the volume flowing through the arc length per hour is vdl, at this time, the air temperature rises from the initial temperature T0 to the average temperature T of the arc. c , convection heat dissipation power p k equal:

[0066]

[0067] Under standard atmospheric pressure, c is expressed as:

[0068]

[0069] Substitute c into the convection heat dissipation power p k Formula, we get:

[0070]

[0071] Wherein, v represents the moving speed of the train, in cm / s, d represents the arc column diameter, in cm, and l represents the arc length, in cm;

[0072] After unit conversion, we get:

[0073]

[0074] Among them, p loss is the heat loss, v is the train speed, d is the arc diameter, l is the arc length, T h is the maximum temperature of the arc column when the arc is burning, T l is the lowest temperature of the arc column when the arc is burning, and T0 is the temperature when the fluid medium is not in contact with the arc;

[0075] As one of the classic arc models, the Schwarz arc model sets the dissipated power and time constant as a power function of the arc conductivity. Compared with the traditional Mayr arc model, the Schwarz arc model is more consistent with the actual arc combustion process. The formula of the classic Schwarz arc model used in this embodiment is:

[0076]

[0077] Where d is the arc diameter, g is the arc conductivity, t is the time, τ is the constant coefficient of the arc time constant, a is the conductivity index of the arc time constant, P lossis the dissipated power, b is the conductivity index of the dissipated power, u is the instantaneous value of the arc voltage, and i is the instantaneous value of the arc current;

[0078] Step 2: Establish an improved Schwarz low-pressure arc electrical characteristic model

[0079] Based on the classic Schwarz arc model, the relevant equations of the pantograph arc under different air pressures at high altitudes are established, namely the improved Schwarz low-pressure arc electrical characteristic model. Combined with the formulas in step 1, the improved Schwarz low-pressure arc electrical characteristic model formula is:

[0080]

[0081] Among them, v is the train speed, which is set to 160 km / h, g is the arc conductivity, and the initial arc conductivity is selected as 10 4 s, τ is the arc time constant coefficient, set to 10 -3 s, in this embodiment, the arc time constant is selected as 10 -4 s, a is the conductivity index of the arc time constant, which is 0.177, u is the instantaneous value of the arc voltage, i is the instantaneous value of the arc current, b is the conductivity index of the dissipated power, which is 0.5, d is the arc diameter, which changes with the altitude, in cm, l is the arc length, assuming the initial arc length is 0.5 cm, T h is the maximum temperature of the arc column when the arc is burning, which varies with the altitude, T l is the lowest temperature of the arc column when the arc is burning, and its value is 4000K; T0 is the temperature of the fluid medium when it is not in contact with the arc, and its value is 300K;

[0082] As one of my country's key projects, the Sichuan-Tibet Railway is of great significance in promoting economic development in central and western China;

[0083] By consulting the data, we know that the Sichuan-Tibet Railway passes through western Sichuan to Tibet. The average altitude of Kangding in western Sichuan is 2500-3000m. The average altitude is 2700m, corresponding to the air pressure P=70.6kPa. The altitude of some lines in Tibet is 4000-5000m. The average altitude is 4500m, corresponding to the air pressure P=50.5kPa, and compared with the standard atmospheric pressure P0=101.3kPa, the arc voltage waveform of the Schwarz model under different air pressures is compared as follows Figure 2 As shown by Figure 2 It can be seen that the arc voltage of the bow-catenary increases with the increase of altitude and the decrease of air pressure, and the increase is the largest at the arcing peak;

[0084] Step 3: Establish the electric locomotive traction drive system model

[0085] The high-speed train traction drive system is a highly integrated and complex power electronic system. Its core components include on-board transformers, traction converters (including rectifiers, intermediate DC side support capacitors, traction inverters) and traction motors. This system ensures that the train can run efficiently and stably through precise power conversion and control. Its principle block diagram is shown below. Figure 3 As shown, during the operation of the train, the train obtains single-phase AC power with a voltage of 25kV and a frequency of 50Hz from the traction contact network through the sliding contact of the roof pantograph, and transmits it to the primary winding of the on-board transformer through the vacuum circuit breaker (VCB) through the high-voltage cable. The traction winding of the on-board transformer outputs electric energy with a voltage of 1.5kV and a frequency of 50Hz, which is transmitted to the rectifier. After rectification, stable high-voltage DC power is output through the intermediate support capacitor, and then supplied to the inverter. The inverter outputs three-phase AC power with adjustable voltage and frequency to control the speed and torque of the traction motor. The torque and speed output by the motor shaft are transmitted to the wheels through the gears of the gearbox, and converted into the traction force of the wheel flange through the friction between the wheel flange and the rail.

[0086] This embodiment takes the actual CRH2 train EMU as a reference, combines the traction braking characteristics of the EMU and the technical parameters of various components including the on-board transformer, rectifier, inverter and three-phase load, to establish an electric locomotive traction drive system model. The specific modeling process is as follows:

[0087] First, the composition of the EMU traction drive system is clarified, including the main components such as the on-board transformer, rectifier, inverter, traction motor, etc., to determine the system architecture, and then collect the technical parameters of each component, such as the rated capacity, ratio, and impedance of the on-board transformer, the control strategy, switching frequency of the rectifier, the control strategy and modulation method of the inverter, the type, rated power, and speed range of the traction motor, etc. Then, according to the collected technical parameters of each component, the corresponding mathematical model is established. For example, the on-board transformer can be represented by an equivalent circuit model, the rectifier and inverter can be represented by a switching function model, and the traction motor can be represented by a dynamic equation model. Then, the control strategy of the traction drive system is designed, including the control logic of the rectifier and inverter, and the speed and torque control strategy of the traction motor. Then, a simulation platform is built using simulation software (such as MATLAB / Simulink), and the mathematical models and control strategies of each component are integrated into the simulation environment. Then, tests are carried out on the simulation platform to simulate different operating conditions, such as starting, acceleration, cruising, braking, etc., and observe the dynamic response of the system. Finally, the simulation results are analyzed, the performance bottleneck of the system is identified, and optimization measures are proposed, such as improving the control strategy and adjusting component parameters.

[0088] The CRH2 train EMU uses an ATM9 transformer, whose rated parameters are shown in Table 1. The rectifier uses a single-phase three-level PWM pulse rectifier, and the inverter uses a three-level inverter. The rectifier, support capacitor, and inverter are packaged as a traction converter. The leakage inductance on the converter input side is 4.3mH.

[0089] Table 1 Rated parameters of vehicle-mounted transformer

[0090]

[0091] Step 4: Build a low-pressure pantograph-catenary arc traction drive system model and conduct simulation analysis

[0092] The improved Schwarz low-pressure arc electrical characteristic model is combined with the electric locomotive traction drive system model to build a low-pressure pantograph-catenary arc traction drive system model. The model structure is as follows: Fig.10 As shown, a simulation analysis is performed to obtain the influence of the pantograph-catenary arc on the train traction drive system under high altitude and low air pressure;

[0093] Based on the simulation analysis of the traction drive system model with low-pressure bow-net arc action, the overvoltage amplitude and harmonic distribution characteristics of the plateau power system are obtained, and the resistance and capacitance parameters and topological structure of the power electronic equipment of the plateau electric locomotive are optimized to ensure the safe and stable operation of the plateau electric locomotive.

[0094] When the pantograph and the catenary are offline during the actual operation of a high-speed train, an arc is generally generated. The arc serves as a freewheeling channel to provide energy to loads such as the on-board transformer. When the pantograph and the catenary are offline for a long time or the train current passes through zero, the arc is quenched due to insufficient energy, which will cause an electrical transient process in the traction circuit. In order to accurately describe the pantograph and the catenary offline process under different conditions during stable operation of the train, this embodiment determines two typical working conditions encountered when the pantograph and the catenary are offline during constant speed operation of the train:

[0095] 1) Set the bow-cat offline time to 100ms, and the bow-cat arc will continue to burn during the offline process;

[0096] 2) The pantograph-catcher offline time is set to 400ms. During the offline process, the arc power dissipation of the pantograph-catcher gradually increases, so that in the later stage of the offline process, the pantograph-catcher is in an extinguished state due to insufficient input energy, and the train loses current;

[0097] According to the two typical working conditions, the short-term offline time of the bow network is set to 100ms, and the long-term offline time of the bow network is set to 400ms. According to the starting time of the motor, the bow network offline time t=0.5s is set, and the offline recovery time is t=0.6s and t=0.9s respectively. Three air pressure environments P0=101.3kPa, P=70.6kPa, and P=50.5kPa are set. The influence of the bow network arc on the high-voltage side voltage of the vehicle transformer and the waveform of the rectifier output voltage changing with time under three air pressure levels is simulated. The simulation results are as follows:

[0098] Figure 4 The waveforms of the voltage on the high-voltage side of the on-board transformer changing with time at the pressure levels of 101.3kPa, 70.6kPa, and 50.5kPa when the bow-net offline time is 100ms. Before the bow-net is offline, the voltage value on the high-voltage side of the on-board transformer is stable at 35kV. After the bow-net is offline, the voltage on the high-voltage side of the on-board transformer does not fluctuate or drop significantly, and remains at around 35kV. As time goes by, this voltage value remains almost unchanged, but there is an obvious drop at the voltage zero point, and the waveform is distorted.

[0099] Figure 5 This is an enlarged view of the voltage waveform on the high-voltage side of the on-board transformer during the arcing process of the bow-net offline. The air pressure has an important influence on the voltage on the high-voltage side of the on-board transformer. The lower the air pressure, the more obvious the voltage drop at the voltage zero point on the high-voltage side of the on-board transformer, and the more serious the waveform distortion. When the air pressure level is 101.3kPa (standard atmospheric pressure), the maximum voltage drop is 5.75kV, when the air pressure level is 70.6kPa, the maximum voltage drop is 10.96kV, and when the air pressure level is 50.5kPa, the maximum voltage drop is 16.44kV. Comparing the two air pressure levels of 50.5kPa and 101.3kPa, the maximum voltage drop increases by 185.91%, which may have a certain impact on the stability of train operation.

[0100] Figure 6 The waveforms of the voltage on the high-voltage side of the on-board transformer changing with time at 101.3kPa, 70.6kPa, and 50.5kPa pressure levels when the bow-net is offline for 400ms. Before the bow-net is offline, the waveform is the same as when it is offline for a short time, and the voltage is stable at about 35kV. After the bow-net is offline and the arc is ignited, a voltage drop and voltage distortion also occur at the voltage zero point, and the drop degree is the same as when it is offline for a short time. When the arc is extinguished due to insufficient input energy, the channel of the load current is cut off, resulting in an impact current in the winding coil of the on-board transformer with a phase opposite to the original current, thereby inducing a recoil overvoltage on the high-voltage side of the on-board transformer, followed by a three-cycle square wave decreasing waveform. As time goes on, the voltage waveform presents a sinusoidal decreasing oscillation waveform until it approaches zero.

[0101] Figure 7 This is an enlarged view of the voltage waveform on the high-voltage side of the on-board transformer during the arc extinction process. The air pressure has an important influence on the voltage on the high-voltage side of the on-board transformer. The lower the air pressure, the greater the voltage change during the arc extinction process, and the greater the overvoltage on the high-voltage side of the on-board transformer. When the air pressure level is 101.3kPa, the overvoltage value is 46.41kV, when the air pressure level is 70.6kPa, the overvoltage value is 49.37kV, and when the air pressure level is 50.5kPa, the overvoltage value is 50.88kV. Compared with the two air pressure levels of 50.5kPa and 101.3kPa, the overvoltage value increases by 9.63%, which may have an impact on the traction converter components and threaten the safe operation of the train.

[0102] Figure 8 The waveform of the DC side voltage changing with time in a short-time offline condition. Fig. 9 The waveform of the DC side voltage changing with time in the case of long-term offline is given by Figure 6 It can be seen that under different air pressure environments, the DC side voltage is basically the same. When the pantograph-catenary contact is good, the voltage value is about 3kV. During the arcing stage of the pantograph-catenary offline, the DC side voltage remains at about 3kV and remains unchanged. It can be seen that when the pantograph-catenary is offline for a short time, due to the continuous burning of the pantograph-catenary arc, the DC side voltage does not change much during the entire process of the pantograph-catenary offline and contact recovery. Fig. 9 It can be seen that when the bow network is offline for a long time, before the arc is extinguished, the waveform is the same as the short-time offline situation, and the voltage is stable at 3kV. After the arc is extinguished, most of the energy stored in the winding coil will be consumed within two cycles, causing the DC voltage output by the rectifier to drop rapidly to zero, and an overvoltage is generated when the bow network re-contacts, and its value is about 7.46kV, and then gradually stabilizes at 3kV. Comparing the three different air pressure levels, the overvoltage values ​​are all around 7.46kV. In the process of rapid drop of DC side voltage, the lower the air pressure, the slower the DC side voltage drops. In the DC side recovery link, the lower the air pressure, the slower the DC side voltage recovers, and there is a lag.

[0103] Under the condition that the model parameters of the traction transmission system under the action of low-pressure pantograph arc are set unchanged, the voltage harmonic distribution of the high-voltage side of the on-board transformer is analyzed under the conditions that the pantograph offline time is t=400ms and the pressure levels are 101.3kPa, 70.6kPa and 50.5kPa respectively. In order to intuitively compare the voltage harmonic distribution of the high-voltage side of the on-board transformer during the change of the pantograph state under the three pressure levels, Fig.11 , Fig.12 , Fig.13 and Fig.14 As shown, this embodiment divides the entire process into three key stages, namely:

[0104] Initial arcing stage (t = 0.50 ~ 0.52s): In this stage, the bow and the catenary begin to separate and the bow and the catenary arc is initially formed;

[0105] Stable arc burning stage (t = 0.60 ~ 0.62s): the arc burns stably and the bow-cat is in a continuous offline stage;

[0106] Arc extinction stage (t = 0.70 ~ 0.72s): As the energy is gradually consumed, the arc is in the extinction stage;

[0107] A fast Fourier transform analysis is performed for each stage to analyze the harmonic characteristics of the high-voltage side voltage of the vehicle transformer, thereby obtaining the harmonic distribution of the high-voltage side voltage of the vehicle transformer. The horizontal axis is the harmonic order, and the vertical axis is the harmonic amplitude percentage, which is the percentage of each harmonic amplitude to the fundamental amplitude. The voltage total harmonic distortion (abbreviated as THD, symbol λ) THD ) can be expressed by the formula:

[0108]

[0109] Among them, U1 is the fundamental amplitude of the voltage, U h is the subharmonic amplitude of voltage, h=1, 2,…,M.

[0110] Fig.11 is the voltage harmonic distribution of the high-voltage side of the on-board transformer at the initial arcing stage under different pressure levels. Fig.11 It can be seen that the harmonic distribution trends under the three air pressure environments are roughly the same. Within the 40th harmonic, the amplitude percentage of the odd harmonics gradually decreases with the increase of the harmonic order, while the amplitude percentage of the even harmonics shows a trend of first increasing and then decreasing. On the whole, the amplitude of the even harmonics is relatively small, and the impact on the voltage waveform is not as significant as that of the odd harmonics. As the air pressure decreases, the amplitude of the fundamental wave decreases slightly, and the amplitude of the same harmonic, especially the amplitude of the low-order harmonic, increases significantly. This shows that in a low-pressure environment, the arc combustion is more unstable and more harmonic components are generated. The total harmonic distortion rate also increases significantly with the decrease in air pressure. When the air pressure level drops from 101.3kPa to 50.5kPa, the total harmonic distortion rate increases from 3.08% to 8.05%, which shows that in a low-pressure environment, the harmonic distortion of the voltage waveform is more obvious;

[0111] Fig.12The harmonic distribution of the high-voltage side voltage of the on-board transformer in the stable arcing stage under different gas pressure levels. From 12, it can be seen that the main energy is concentrated in the low-frequency band, the amplitude of the low-frequency harmonics is significantly higher than that of the high-frequency harmonics, and the amplitude of the odd harmonics is significantly higher than that of the even harmonics, which is mainly manifested in low-order odd harmonics (such as 1st, 3rd, 5th, 7th, etc.). Within the 80th harmonic, as the number of harmonics increases, the percentage of the amplitude of the odd harmonics shows a trend of first decreasing and then increasing, and the percentage of the amplitude of the even harmonics shows a trend of first increasing and then decreasing;

[0112] As the air pressure decreases, the fundamental wave amplitude decreases slightly. The amplitudes of the same harmonics, especially the low-order harmonics, also increase significantly under different air pressures. The total harmonic distortion rate increases as the air pressure decreases. When the voltage level drops from the standard atmospheric pressure of 101.3kPa to 50.5kPa, the total harmonic distortion rate increases from 5.06% to 11.12%, indicating that in a low-pressure environment, the influence of harmonics is more significant and the harmonic components are more complex.

[0113] Fig.13 is the voltage harmonic distribution of the high-voltage side of the on-board transformer during the arc extinction stage at different pressure levels. Fig.13 It can be seen that the main energy is concentrated in the low-frequency harmonics within the 20th order, and the harmonics after the 60th order are close to 0, which means that there is a large DC component in the arc extinction stage, the power loss is large, the odd harmonics are significantly higher than the even harmonics, and the odd and even harmonics show a downward trend as a whole;

[0114] and Fig.11 and Fig.12 The difference between the two stages shown is that in the arc extinction stage, as the air pressure decreases, the fundamental amplitude increases significantly. This may be due to the large changes in voltage and current during the arc extinction process. The lower the air pressure, the greater the change, which affects the fundamental amplitude. As the air pressure decreases, the total harmonic distortion rate also increases. When the air pressure level drops from the standard atmospheric pressure of 101.3kPa to 50.5kPa, the total harmonic distortion rate increases from 28.32% to 36.49%. This shows that as the air pressure decreases, the harmonic distortion in the train system becomes more serious, which may have a significant impact on the reliability of the system.

[0115] Fig.14 The variation trend of the total harmonic distortion rate of the high-voltage side voltage of the traction drive system transformer at different arcing stages under different gas pressure levels is shown in Figure 2. Fig.14It can be seen that when the bow and the catenary are in contact, the total harmonic distortion rate is close to 0 and the voltage is relatively stable. In the bow-catenary arcing stage, as the arcing time increases, the total harmonic distortion rate shows a slowly increasing trend. The lower the air pressure, the greater the corresponding total harmonic distortion rate. In the bow-catenary arc extinguishing link, the total harmonic distortion rate increases rapidly. When the air pressure level drops from the standard atmospheric pressure 101.3kPa to 50.5kPa, the total harmonic distortion rate increases from 28.32% to 36.49%, indicating that the drop in air pressure causes the input voltage waveform to be distorted, deteriorating the power quality, which may threaten the safety and stability of train operation in high-altitude and low-pressure environments.

[0116] Based on the above simulation analysis, the following conclusions are drawn:

[0117] 1) When the pantograph network is offline for a short time, the voltage on the high-voltage side of the on-board transformer drops at the voltage zero crossing, and the waveform is distorted. When P0=101.3kPa, the maximum drop voltage is 5.75kV, when P=70.6kPa, the maximum drop voltage is 10.96kV, and when P=50.5kPa, the maximum drop voltage is 16.44kV. When the air pressure level drops from the standard atmospheric pressure of 101.3kPa to 50.5kPa, that is, when the altitude rises from 0m to 4500m, the maximum drop voltage increases by 185.91%. The lower the air pressure, the greater the voltage drop and the more serious the waveform distortion, resulting in short-term voltage fluctuations in the train transmission system, affecting the normal operation of the train;

[0118] 2) When the bow network is offline for a long time, after the arc continues to burn for a period of time, the arc goes out, the DC side voltage of the traction converter drops rapidly, and overvoltage is generated when it is restored offline. The lower the air pressure, the slower the DC side voltage drops and recovers, and overvoltage is generated on the high-voltage side of the on-board transformer. When P0=101.3kPa, the overvoltage value is 46.41kV, when P=70.6kPa, the overvoltage value is 49.37kV, when P=50.5kPa, the overvoltage value is 50.88kV, when the air pressure drops from the standard atmospheric pressure of 101.3kPa to the air pressure of 50.5kPa corresponding to an altitude of 4500m, the overvoltage value increases by 9.63%. The lower the air pressure, the greater the overvoltage, which may increase the safety risk of train operation in a high-altitude and low-pressure environment, posing a safety hazard;

[0119] 3) Under different air pressure conditions, the influence of the bow-net arc on the harmonic distribution characteristics of the voltage on the high-voltage side of the on-board transformer is different. In the initial arcing stage and the stable arcing stage, the lower the air pressure, the greater the total harmonic distortion rate. In the arc extinction stage, due to the large changes in voltage and current, the lower the air pressure, the fundamental amplitude shows a significant upward trend, and the total harmonic distortion rate is also greater. When the air pressure level is 50.5kPa, that is, the altitude is 4500m, the total harmonic distortion rate reaches 36.49%, and there are a large number of DC components. This shows that in the high-altitude and low-pressure environment, the harmonic distortion of the voltage waveform is more obvious, which may have a greater impact on the stability of the power system and the operation of the equipment.

[0120] The present invention establishes a low-pressure pantograph-catenary arc-action traction transmission system model suitable for high-altitude and low-pressure environments. It can accurately analyze the influence of the pantograph-catenary offline arc on the electrical characteristics of the high-speed train on-board transformer and traction converter under different altitude pressures, and obtain the voltage harmonics at different stages. It can accurately reflect the actual operating conditions of the traction transmission system under high-altitude and low-pressure environments, provide a model reference and research basis for the design of plateau electric locomotives and the parameter design of plateau electric locomotive electronic devices, and ensure the safe and stable operation of plateau electric locomotives.

[0121] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for establishing a traction transmission system model of low-pressure pantograph-catenary arc action, characterized in that: The following steps are involved: Step 1: Based on the classic Schwarz arc model, the arc dissipation power is corrected by combining the air pressure environment parameters, running speed, arc length parameters and arc temperature parameters of the train in high altitude areas; Step 2: Based on the classic Schwarz arc model, establish the relevant equations of the arc of the train bow network under different air pressures at high altitudes, that is, the improved Schwarz low-pressure arc electrical characteristic model. The formula of the improved Schwarz low-pressure arc electrical characteristic model is: ； in, v is the train running speed, g is the arc conductance, τ is the arc time constant coefficient, a is the conductivity index of the arc time constant, u is the instantaneous value of the arc voltage, i is the instantaneous value of the arc current, d is the arc diameter, l is the arc length, T h is the maximum temperature of the arc column when the arc is burning, T l is the lowest temperature of the arc column when the arc is burning, T 0 is the temperature when the fluid medium is not in contact with the arc; Step 3: Taking the actual train EMU as a reference, combined with the traction braking characteristics of the EMU and the technical parameters of various components including the on-board transformer, rectifier, inverter and three-phase load, establish the electric locomotive traction drive system model; Step 4: Combine the improved Schwarz low-pressure arc electrical characteristic model with the electric locomotive traction drive system model, build a low-pressure pantograph-catenary arc traction drive system model and perform simulation analysis to obtain the impact of the pantograph-catenary arc on the train traction drive system under high-altitude and low-pressure conditions.

2. The method for establishing a low-pressure pantograph-catenary arc action traction transmission system model according to claim 1 is characterized by: In the step 1, the formula of the classic Schwarz arc model is: ； in, d is the arc diameter, g is the arc conductance, t For time, τ is the arc time constant coefficient, a is the conductivity index of the arc time constant, P loss is the dissipated power, b is the conductivity index of the dissipated power, u is the instantaneous value of the arc voltage, i is the instantaneous value of the arc current.

3. The method for establishing a low-pressure pantograph-catenary arc action traction transmission system model according to claim 1, characterized in that: In step 1, the specific steps for correcting the arc dissipation power are as follows: firstly, the atmospheric pressure data of different regions are analyzed to obtain the altitude. H With air pressure P The relationship between them is as follows: ； in, P 0 is the atmospheric pressure in the plain area. As the air pressure decreases, the arc diameter increases. The relationship between the two is as follows: ； During the arc burning process, the arc dissipates power p loss By conduction power p t , Convection heat dissipation power p k and radiated power p s The corresponding expression is: p loss = p t + p k + p s Since the arc burning freely in the atmosphere will dissipate most of its heat energy through the convection mechanism, this process accounts for more than 80% of the total heat loss, while the heat conduction and radiation losses of the arc account for a relatively small proportion, so the conduction power and radiation power losses are ignored. When the pantograph is separated from the contact network, the front end of the high-speed train meets the air, resulting in air compression, that is, the air is compressed at the front end of the train to produce a high-pressure area. The high-pressure air then rapidly diffuses to the sides and top of the vehicle, forming lateral and upward airflows, further strengthening the convection heat dissipation of the pantograph-catenary arc. Therefore, the convection heat dissipation power is regarded as the dissipation power of the pantograph-catenary arc, that is: p loss = p k Based on the arc blowing theory, the arc blowing direction is classified as horizontal blowing when the airflow is perpendicular to the arc axis, and longitudinal blowing when the airflow is parallel to the arc direction. During the train operation, the arc is perpendicular to the train operation direction and is mainly affected by horizontal arc blowing. Therefore, the influence of longitudinal arc blowing on the electrical characteristics of the pantograph-catenary arc is ignored. Assume that the train speed is v , the arc diameter is d , the volume flowing through the arc length per hour is vdl At this time, the air temperature is T 0 rises to the average temperature of the arc T c , Convection heat dissipation power p k equal: ； At standard atmospheric pressure, c It is expressed as: ； Will c Substitute the convection heat dissipation power p k Formula, we get: ； in, v Indicates the moving speed of the train in cm / s. d Indicates the arc column diameter in cm. Indicates the arc length in cm; After unit conversion, we get: ； in, p loss For heat loss, v is the train running speed, d is the arc diameter, l is the arc length, T h is the maximum temperature of the arc column when the arc is burning, T l is the lowest temperature of the arc column when the arc is burning, T 0 is the temperature of the fluid medium when it is not in contact with the arc.

4. The method for establishing a low-pressure pantograph-catenary arc action traction transmission system model according to claim 1, characterized in that: In the step three, the actual train EMU used as reference is a CRH2 EMU, which uses an ATM9 transformer, a rectifier of the CRH2 EMU uses a single-phase three-level PWM pulse rectifier, and an inverter of the CRH2 EMU uses a three-level inverter. The rectifier, support capacitor and inverter are integrally packaged into a traction converter.

5. The method for establishing a low-pressure pantograph-catenary arc action traction transmission system model according to claim 3 is characterized by: In the step four, during the simulation analysis, two typical operating conditions encountered when the train is running at a constant speed and the bow-catcher is offline are determined. In the first typical operating condition, the bow-catcher offline time is set to 100ms, and the bow-catcher arc continues to burn during the offline process. In the second typical operating condition, the bow-catcher offline time is set to 400ms, and the power dissipation of the bow-catcher arc gradually increases during the offline process.

6. The method for establishing a low-pressure pantograph-catenary arc action traction transmission system model according to claim 5, characterized in that: According to the two typical working conditions, the short-term offline time of the bow-net is set to 100ms and the long-term offline time of the bow-net is set to 400ms. According to the starting time of the motor, the bow-net offline time is set to t=0.5s, and the offline recovery time is set to t=0.6s and t=0.9s respectively. P 0=101.3kPa, P =70.6kPa, P =50.5kPa three kinds of air pressure environment, the simulation obtains the influence of the bow-net arc on the waveform of the high-voltage side voltage of the vehicle transformer and the rectifier output voltage changing with time under three air pressure levels.

7. The method for establishing a low-pressure pantograph-catenary arc action traction transmission system model according to claim 6, characterized in that: Under the condition that the model parameters of the traction transmission system with low-pressure pantograph-catenary arcing are the same, fast Fourier transform analysis is performed on the high-voltage side voltage of the on-board transformer when the pantograph-catenary offline time is 400ms at the air pressure levels of 101.3kPa, 70.6kPa and 50.5kPa respectively.

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